Methods for high-precision gap and orientation sensing between a transparent template and substrate for imprint lithography

ABSTRACT

Described are high precision gap and orientation measurement methods between a template and a substrate used in imprint lithography processes. Gap and orientation measurement methods presented here include uses of broad-band light based measuring techniques.

PRIORITY CLAIM

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/222,233 filed on Aug. 1, 2000 entitled “Methods forHigh-Precision Gap and Orientation Sensing between a TransparentTemplate and Substrate for Imprint Lithography.”

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms ofN66001-98-18914 awarded by the Defense Advanced Research Projects Agency(DARPA).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods and systems of achieving highprecision gap and orientation measurements in imprint lithography.

2. Description of the Relevant Art

Imprint lithography is a technique that is capable of printing featuresthat are smaller than 50 nm in size on a substrate. Imprint lithographymay have the potential to replace photolithography as the choice forsemiconductor manufacturing in the sub-100 nm regime. Several imprintlithography processes have been introduced during 1990s. However, mostof them have limitations that preclude them from use as a practicalsubstitute for photolithography. The limitations of these priortechniques include, for example, high temperature variations, the needfor high pressures and the usage of flexible templates.

Imprint lithography processes may be used to transfer high resolutionpatterns from a quartz template onto substrate surfaces at roomtemperature and with the use of low pressures. In the Step and FlashImprint Lithography (SFIL) process, a rigid quartz template is broughtinto indirect contact with the substrate surface in the presence oflight curable liquid material. The liquid material is cured by theapplication of light and the pattern of the template is imprinted intothe cured liquid.

Imprint lithography processes can be used to manufacture single andmulti-layer devices. Single layer devices, may be manufactured byforming a thin layer of material into desired features on a substrate.To produce devices having a feature size below 100 nm, an imprintedlayer thickness may be less than ¼ of the mean wavelength of a broadbandlight. The imprinted layer should also be substantially planar. Thus, itis desirable to have accurate and rapid methods of measuring the gap andthe orientation between a template and a substrate during an imprintlithographic process.

More specifically, for the purpose of imprint lithography, gap andorientation measurement processes need to facilitate gap measurement inthe range of less than 10 nm to 30 μm. Gap measurements, therefore,should be achieved without contacting the template and substrate andwith a resolution of less than 10 nm.

SUMMARY OF THE INVENTION

The embodiments described herein include methods and systems that areapplicable for gap sensing in imprint lithography processes.

In certain embodiments, methods of determining the spacing between atemplate and a substrate may include positioning the template and thesubstrate in a spaced relationship to one another such that a gap iscreated between the template and the substrate. Light having a pluralityof wavelengths may be applied to the template and the substrate. Lightreflected from a surface of the template and the substrate may bemonitored. For example, light reflected from the surface of the templateand the substrate may be monitored for variations in the intensity ofthe light across a range of wavelengths. The distance between thesurface of the template and the substrate may be determined based on themonitored light. Some embodiments may further include determining anerror signal that corresponds to the difference between a desireddistance between the surface of the template and the substrate and thedetermined distance between the surface of the template and thesubstrate. The error signal may be used to control one or moreactuators. The one or more actuators may be configured to adjust thedistance between the template and the substrate.

In some embodiments, the one or more actuators may be configured toadjust the relative position of the surface of the template and thesubstrate to achieve a substantially parallel configuration. In suchembodiments, the method may include determining the distance between thesurface of the template and the substrate at three or more non-colinearpositions. The error signal may be determined based on the three or moredistances determined.

In an embodiment, a template suitable for use in methods and systemsdisclosed herein may be a patterned template, or a substantially planartemplate. A patterned template may be used to transfer a pattern to asubstrate. A substantially planar template may be used to planarize apatterned substrate. The template may include one or more gap sensingsections. For example, the gap sensing sections may include a pluralityof recesses on a surface of the template. The recesses may be of a knowndepth. For example, the depth of each recess may be at least ¼ of themean wavelength of the light applied to the template and the substrate.The light applied to the template and the substrate may be passedthrough the gap sensing sections of the template. The template may beformed of materials including, but not limited to: quartz, indium tinoxide, and SiOx where X is less than 2. For example, X may be about 1.5.

In an embodiment, a substrate suitable for use in methods and systemsdisclosed herein may be a semiconductor wafer. The substrate may beformed of materials including, but not limited to: silicon, gallium,germanium, indium, quartz, sapphire, silicon dioxide, polysilicon, orother dielectric materials. Additionally, the substrate may include oneor more layers on a surface of the substrate. The refractive index ofeach layer on the surface of the substrate may be known. In such cases,the method may include determining a thickness of each layer on thesurface of the substrate.

Embodiments disclosed herein also include methods of forming a patternon a substrate using a template that is transparent to an activatinglight. Such embodiments may be used, for example, to form asemiconductor device. In some embodiments, the substrate may bepatterned. In such embodiments, a substantially planar template may beused to form a substantially planar region on the substrate. In otherembodiments, the template may be patterned. In such embodiments, thepatterned template may be used to form a pattern on the substrate.

In an embodiment, a method of forming a pattern on a substrate using atemplate that is transparent to an activating light may include applyingan activating light curable liquid to a portion of the substrate. Thetemplate and the substrate may be positioned in a spaced relationship toone another such that a gap is created between the template and thesubstrate. In some embodiments, the distance between the template andthe substrate may be determined using a light based measuring device. Insome embodiments, the distance between the template and the substratemay be monitored using a light based measuring device. In suchembodiments, the position of the template with respect to the substratemay be adjusted while monitoring the distance between the template andthe substrate such that the template and the substrate are positioned ata predetermined distance from each other. Activating light may beapplied through the template to the liquid. The application ofactivating light may substantially cure the liquid. In an embodiment, apattern of a patterned template may be formed in the cured liquid. Forexample, the template may include a pattern having at least somefeatures that are less than 250 nm in size. After the template isseparated from the cured liquid, the cured liquid may have at least somefeatures less than about 250 nm in size. In another embodiment, thecured liquid may form a substantially planar region on the substrate.The method may also include separating the template from the curedliquid.

The activating light curable liquid may be applied to the substrateusing one or more fluid dispensers. While the activating light curableliquid is being dispensed, the substrate may be moved with respect tothe fluid dispenser such that a predetermined pattern is created. Thepredetermined pattern may be a pattern that is configured to inhibit theformation of air bubbles in the liquid when the template contacts theliquid as the template and substrate are positioned in a spacedrelation. In addition, the predetermined pattern may be selected suchthat the liquid fills the gap in an area substantially equal to thesurface area of the template, if the template includes a pattern.Alternately, if the substrate is patterned, the pattern may be selectedsuch that the liquid fills the gap in an area substantially equal to thesurface area of the substrate.

Positioning the template and the substrate in a spaced relationship mayinclude positioning the template over the substrate, and moving thetemplate toward the substrate until a desired spaced relationship isachieved. As the template is moved toward the substrate, the liquid onthe substrate may substantially fill the gap between the template andthe substrate. In an embodiment, the desired spaced relationship may besuch that the template is at a distance of less than about 200 nm fromthe substrate. In some embodiments, positioning the template and thesubstrate in a spaced relationship may include determining an errorsignal. The error signal may correspond to the difference between adesired distance between the surface of the template and the substrateand the determined distance between the surface of the template and thesubstrate. The error signal may be sent to at least one actuator. The atleast one actuator may be configured to position the template and thesubstrate in a spaced relationship to one another. In an embodiment,positioning the template and the substrate in a spaced relationship mayalso include positioning the template and the substrate in asubstantially parallel orientation.

In some embodiments, positioning the template and the substrate in aspaced relationship may include positioning the template over thesubstrate such that the template is substantially non-parallel to thesubstrate. The template may be moved toward the substrate whileremaining in a substantially non-parallel orientation with respect tothe substrate. When a desired spaced relationship between the templateand the substrate is achieved, the template may be oriented into asubstantially parallel orientation with respect to the substrate.

Determining the distance between the template and the substrate using alight based measuring device may include applying light to the templateand the substrate. The light may include a plurality of wavelengths.Light reflected from a surface of the template and the substrate may bemonitored. The distance between the template and the substrate may bedetermined based on the monitored light. To determine the distancebetween the template and the substrate, the method may include obtainingdata representative of the intensity of at least some of the wavelengthsof light reflected. A wavenumber may be calculated based on the data,where the wavenumber is a function of the refractive index of a materialdisposed between the template and the substrate and the wavelength ofthe refractive light. The distance between the template and thesubstrate may then be calculated. The distance between the template andthe substrate may be a function of the wavenumber and the intensity ofreflected light corresponding to the wavenumber. Calculating thedistance between the template and the substrate may include determininga Fourier Transform of the wavenumber and intensity data. In someinstances, the method may also include determining at least one localmaximum or local minimum of the data after performing the FourierTransform.

In some embodiments, determining the distance between the template andthe substrate may include determining the distance at 3 or morenon-colinear locations, and further include determining whether thesurface of the template and substrate are substantially parallel basedon the 3 or more distance determinations. One or more actuators may beconfigured to adjust the relative position of the surface of thetemplate and the substrate to achieve a substantially parallelconfiguration. In such embodiments, the method may include determiningan error signal based on the three or more distances determined. Theerror signal may be sent to the one or more actuators. The actuators mayadjust the relative position of the template and the substrate toachieve a substantially parallel configuration.

An activating light curable liquid suitable for use in embodimentsdisclosed herein may be an ultraviolet light curable composition. Theactivating light curable liquid may be a photoresist material.

Separating the template from the cured liquid may include moving thetemplate to a substantially non-parallel orientation and moving thetemplate away from the substrate.

In some embodiments, a method of forming a pattern on a substrate usinga template may include forming a transfer layer on the substrate priorto applying the liquid to the substrate. The transfer layer may beetched after separating the patterned template from the substrate.Etching the transfer layer may impart the pattern to the transfer layer.

A system for forming a pattern on a substrate using a template mayinclude, but is not limited to:

-   -   a top frame;    -   an orientation stage coupled to the top frame;    -   a substrate stage below the orientation stage configured to        support the substrate; and    -   a light based measurement device coupled to the top frame.        The orientation stage may include a template support. A template        may be disposed in the template support. The light based        measurement device may be configured to determine a distance        between the template and the substrate. Additionally, one or        more fluid dispensers may be coupled to the top frame.

The orientation stage may further include a first flexure memberconfigured to pivot about a first orientation axis during use and asecond flexure member coupled to the first flexure member configured topivot about a second orientation axis during use. The first orientationaxis may be substantially orthogonal to the second orientation axis. Thetemplate support may be coupled to the second flexure member. Thetemplate support may be configured to hold the template during use. Thesecond flexure member may be coupled to the first flexure member suchthat the template, when disposed in the support, may be moved about apivot point intersected by the first and second orientation axis duringuse.

In certain embodiments, the first flexure member may include first andsecond arms. The first arm may include a first set of flexure jointsconfigured to provide pivotal motion of the first flexure member aboutthe first orientation axis. The second arm may include a second set offlexure joints configured to provide pivotal motion of the first flexuremember about the first orientation axis. Likewise, the second flexuremember may include third and fourth arms. The third arm may include athird set of flexure joints configured to provide pivotal motion of thesecond flexure member about the second orientation axis. The fourth armmay include a fourth set of flexure joints configured to provide pivotalmotion of the second flexure member about the second orientation axis.Actuators may be coupled to the first and second flexure members. Theactuators may be configured to cause pivoting of the first and secondflexure members about the first and second orientation axis,respectively, during use. For example, the actuators may bepiezoelectric actuators. The first flexure member may include a firstopening. The second flexure member may include a second opening. Thetemplate support may include a third opening. Each of the first, secondand third openings may be configured to allow activating light andsensing light to be directed onto the template during use. The first,second and third openings may be substantially aligned when the firstflexure member is coupled to the second flexure member.

The light based measurement device may include at least one opticalprobe configured to direct light through the template. The light basedmeasurement device may include at least one optical probe configured todetect light reflected from the substrate. Either of the optical probesmay be configured to be movable from a first position, above thetemplate, to a second position, away from the template. Alternately,either of the optical probes may be substantially transparent to aselected wavelength of light. For example, the system may include anactivating light source, and selected wavelength of light may correspondto a wavelength of light generated by the activating light source. Thelight based measurement device may also include an electronic imagingdevice. The light based measurement device may include a broad-bandspectrometer or a laser interferometer.

The light based measurement device may include an illumination systemconfigured to direct detecting light through the template during use.The illumination system may be positioned between the template and theactivating light source. The illumination system may be substantiallytransparent to the activating light produced by the activating lightsource. Alternately, the illumination system may be movable such thatthe illumination system may be positionable into a position that is notin optical interference with the activating light source and thetemplate. The light based measurement device may further include adetection system optically coupled to the illumination system. Thedetection system may be configured to detect light reflected from thesubstrate positioned on the substrate stage.

In some embodiments, the substrate may include at least one layer of aknown refractive index on a surface of the substrate. In suchembodiments, the light based measuring device may be further configuredto determine the thickness of the at least one layer on the surface ofthe substrate.

In some embodiments, the template may include an alignment mark. In suchembodiments, the template alignment mark may be complimentary to analignment mark on the substrate.

The system may further include a pre-calibration stage coupled to theorientation stage and the top frame. The pre-calibration stage may beconfigured to move the orientation stage toward and away from thesubstrate during use. The pre-calibration may include at least oneactuator coupled to the orientation stage. The actuator may beconfigured to move the orientation stage toward and away from thesubstrate. The pre-calibration may further include first and secondsupport members. In such embodiments, the at least one actuator may becoupled to the top frame and the second support member. The actuator mayextend through the first support member. The first support member may becoupled to the top frame. The second support member may be coupled tothe first support member and the orientation stage.

The substrate stage may include a vacuum chuck. The vacuum chuck mayinclude a chuck body and a vacuum flow system coupled to the chuck body.The vacuum flow system may be configured to apply a suction force at thesurface of the chuck body during use. The substrate stage may also beconfigured to move the substrate along a plane substantially parallel tothe template.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to theaccompanying drawings in which:

FIGS. 1A and 1B depict a cross-sectional view of the gap between atemplate and a substrate;

FIGS. 2A-2E depict cross-sectional views of an imprint lithographyprocess;

FIG. 3 depicts a process flow chart showing the sequence of steps of theimprint lithography process;

FIG. 4 depicts a bottom view of a patterned template;

FIG. 5 depicts a cross-sectional view of a template positioned over asubstrate;

FIG. 6 depicts a cross sectional view of an imprint lithography processusing a transfer layer;

FIG. 7 depicts a cross-sectional view of a process for forming animprint lithography template;

FIG. 8 depicts a cross-sectional views of patterned templates;

FIG. 9 depicts a cross sectional view of alternate patterned templatedesigns;

FIG. 10 depicts a top view of a process for applying a curable fluid toa substrate;

FIG. 11 depicts a schematic of an apparatus for dispensing a fluidduring an imprint lithographic process;

FIG. 12 depicts fluid dispensing patterns used in an imprintlithographic process;

FIG. 13 depicts a fluid pattern that includes a plurality of drops on asubstrate;

FIG. 14 depicts a schematic of an alternate apparatus for dispensing afluid during an imprint lithographic process;

FIG. 15 depicts a fluid pattern that includes a plurality ofsubstantially parallel lines;

FIG. 16 depicts a projection view of a substrate support system;

FIG. 17 depicts a projection view of an alternate substrate supportsystem;

FIG. 18 is a schematic diagram of a 4-bar linkage illustrating motion ofthe flexure joints;

FIG. 19 is a schematic diagram of a 4-bar linkage illustrating alternatemotion of the flexure joints;

FIG. 20 is a projection view of a magnetic linear servo motor;

FIG. 21 is a process flow chart of global processing of multipleimprints;

FIG. 22 is a process flow chart of local processing of multiple imprints

FIG. 23 is a projection view of the axis of rotation of a template withrespect to a substrate;

FIG. 24 depicts a measuring device positioned over a patterned template;

FIG. 25 depicts a schematic of an optical alignment measuring device;

FIG. 26 depicts a scheme for determining the alignment of a templatewith respect to a substrate using alignment marks;

FIG. 27 depicts a scheme for determining the alignment of a templatewith respect to a substrate using alignment marks using polarizedfilters;

FIG. 28 depicts a schematic view of a capacitive template alignmentmeasuring device;

FIG. 29 depicts a schematic view of a laser interferometer alignmentmeasuring device;

FIG. 30 depicts a scheme for determining alignment with a gap betweenthe template and substrate when the gap is partially filled with fluid;

FIG. 31 depicts an alignment mark that includes a plurality of etchedlines;

FIG. 32 depicts a projection view of an orientation stage;

FIG. 33 depicts an exploded view of the orientation stage;

FIG. 34 depicts a process flow a gap measurement technique;

FIG. 35 depicts a cross sectional view of a technique for determiningthe gap between two materials

FIG. 36 depicts a graphical representation for determining local minimumand maximum of a gap;

FIG. 37 depicts a template with gap measuring recesses;

FIG. 38 depicts a schematic for using an interferometer to measure a gapbetween a template and interferometer;

FIG. 39 depicts a schematic for probing the gap between a template and asubstrate using a probe-prism combination;

FIG. 40 depicts a cross-sectional view of an imprint lithographicprocess;

FIG. 41 depicts a schematic of a process for illuminating a template;

FIG. 42 depicts a projection view of a flexure member;

FIG. 43 depicts a first and second flexure member assembled for use;

FIG. 44 depicts a projection view of the bottom of an orientation stage;

FIG. 45 depicts a schematic view of a flexure arm;

FIG. 46 depicts a cross-sectional view of a pair of flexure arms;

FIG. 47 depicts a scheme for planarization of a substrate;

FIG. 48 depicts various views of a vacuum chuck for holding a substrate;

FIG. 49 depicts a scheme for removing a template from a substrate aftercuring;

FIG. 50 depicts a cross-sectional view of a method for removing atemplate from a substrate after curing;

FIG. 51 depicts a schematic view of a template support system; and

FIG. 52 depicts a side view of a gap between a template and a substrate;

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawing and will herein be described in detail. It shouldbe understood, however, that the drawings and detailed descriptionthereto are not intended to limit the invention to the particular formdisclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments presented herein generally relate to systems, devices, andrelated processes of manufacturing small devices. More specifically,embodiments presented herein relate to systems, devices, and relatedprocesses of imprint lithography. For example, these embodiments mayhave application to imprinting very small features on a substrate, suchas a semiconductor wafer. It should be understood that these embodimentsmay also have application to other tasks, for example, the manufactureof cost-effective Micro-Electro-Mechanical Systems (or MEMS).Embodiments may also have application to the manufacture of other kindsof devices including, but not limited to: patterned magnetic media fordata storage, micro-optical devices, biological and chemical devices,X-ray optical devices, etc.

With reference now to the figures, and specifically to FIGS. 1A and 1B,therein are shown arrangements of a template 12 predisposed with respectto a substrate 20 upon which desired features are to be imprinted usingimprint lithography. Specifically, the template 12 may include a surface14 that fabricated to take on the shape of desired features which, inturn, may be transferred to the substrate 20. In some embodiments, atransfer layer 18 may be placed between the substrate 20 and thetemplate 12. Transfer layer 18 may receive the desired features from thetemplate 12 via imprinted layer 16. As is well known in the art,transfer layer 18 may allow one to obtain high aspect ratio structures(or features) from low aspect ratio imprinted features.

For the purpose of imprint lithography, it is important to maintain thetemplate 12 and substrate 20 as close to each other as possible andnearly parallel. For example, for features that are about 100 nm wideand about 100 nm deep, an average gap of about 200 nm or less with avariation of less than about 50 nm across the imprinting area of thesubstrate 20 may be required for the imprint lithography process to besuccessful. Embodiments presented herein provide a way of controllingthe spacing between the template 12 and substrate 20 for successfulimprint lithography given such tight and precise gap requirements.

FIGS. 1A and 1B illustrate two types of problems that may be encounteredin imprint lithography. In FIG. 1A, a wedge shaped imprinted layer 16results because that the template 12 is closer to the substrate 20 atone end of the imprinted layer 16. FIG. 1A illustrates the importance ofmaintaining template 12 and substrate 20 substantially parallel duringpattern transfer. FIG. 1B shows the imprinted layer 16 being too thick.Both of these conditions may be highly undesirable. Embodimentspresented herein provide systems, processes and related devices whichmay eliminating the conditions illustrated in FIGS. 1A and 1B as well asother orientation problems associated with prior art lithographytechniques.

FIGS. 2A through 2E illustrate an embodiment of an imprint lithographyprocess, denoted generally as 30. In FIG. 2A, template 12 may beorientated in spaced relation to the substrate 20 so that a gap 31 isformed in the space separating template 12 and substrate 20. Surface 14of template 12 may be treated with a thin layer 13 that lowers thetemplate surface energy and assists in separation of template 12 fromsubstrate 20. The manner of orientation and devices for controlling gap31 between template 12 and substrate 20 are discussed below. Next, gap31 may be filled with a substance 40 that conforms to the shape oftreated surface 14. Alternately, in an embodiment, substance 40 may bedispensed upon substrate 20 prior to moving template 12 into a desiredposition relative to substrate 20.

Substance 40 may form an imprinted layer such as imprinted layer 16shown in FIGS. 1A and 1B. Preferably, substance 40 may be a liquid sothat it may fill the space of gap 31 rather easily and quickly withoutthe use of high temperatures and the gap can be closed without requiringhigh pressures. Further details regarding appropriate selections forsubstance 40 are discussed below.

A curing agent 32 may be applied to the template 12 causing substance 40to harden and assume the shape of the space defined by gap 31. In thisway, desired features 44 (FIG. 2D) from the template 12 may betransferred to the upper surface of the substrate 20. Transfer layer 18may be provided directly on the upper surface of substrate 20. Transferlayer 18 may facilitate the amplification of features transferred fromthe template 12 to generate high aspect ratio features.

As depicted in FIG. 2D, template 12 may be removed from substrate 20leaving the desired features 44 thereon. The separation of template 12from substrate 20 must be done so that desired features 44 remain intactwithout shearing or tearing from the surface of the substrate 20.Embodiments presented herein provide a method and associated system forpeeling and pulling (referred to herein as the “peel-and-pull” method)template 12 from substrate 20 following imprinting so that desiredfeature 44 remain intact.

Finally, in FIG. 2E, features 44 transferred from template 12 tosubstance 40 may be amplified in vertical size by the action of thetransfer layer 18 as is known in the use of bilayer resist processes.The resulting structure may be further processed to complete themanufacturing process using well-known techniques. FIG. 3 summarizes anembodiment of an imprint lithography process, denoted generally as 50,in flow chart form. Initially, at step 52, course orientation of atemplate and a substrate may be performed so that a rough alignment ofthe template and substrate may be achieved. An advantage of courseorientation at step 52 may be that it may allow pre-calibration in amanufacturing environment, where numerous devices are to bemanufactured, with efficiency and with high production yields. Forexample, where the substrate includes one of many die on a semiconductorwafer, course alignment (step 52) may be performed once on the first dieand applied to all other dies during a single production run. In thisway, production cycle times may be reduced and yields may be increased.

At step 54, a substance may be dispensed onto the substrate. Thesubstance may be a curable organosilicon solution or other organicliquid that may become a solid when exposed to activating light. Thefact that a liquid is used may eliminate the need for high temperaturesand high pressures associated with prior art lithography techniques.Next, at step 56, the spacing between the template and substrate may becontrolled so that a relatively uniform gap may be created between thetwo layers permitting the precise orientation required for successfulimprinting. Embodiments presented herein provide a device and system forachieving the orientation (both course and fine) required at step 56.

At step 58, the gap may be closed with fine vertical motion of thetemplate with respect to the substrate and the substance. The substancemay be cured (step 59) resulting in a hardening of the substance into aform having the features of the template. Next, the template may beseparated from the substrate, step 60, resulting in features from thetemplate being imprinted or transferred onto the substrate. Finally, thestructure may be etched, step 62, using a preliminary etch to removeresidual material and a well-known oxygen etching technique to etch thetransfer layer.

In various embodiments, a template may incorporate unpatterned regionsi) in a plane with the template surface, ii) recessed in the template,iii) protrude from the template, or iv) a combination of the above. Atemplate may be manufactured with protrusions, which may be rigid. Suchprotrusions may provide a uniform spacer layer useful for particletolerance and optical devices such as gratings, holograms, etc.Alternately, a template may be manufactured with protrusions that arecompressible.

In general, a template may have a rigid body supporting it via surfacecontact from: i) the sides, ii) the back, iii) the front or iv) acombination of the above. The template support may have the advantage oflimiting template deformation or distortion under applied pressure. Insome embodiments, a template may be coated in some regions with areflective coating. In some such embodiments, the template mayincorporate holes in the reflective coating such that light may passinto or through the template. Such coatings may be useful in locatingthe template for overlay corrections using interferometry. Such coatingsmay also allow curing with a curing agent sources that illuminatesthrough the sides of the template rather than the top. This may allowflexibility in the design of a template holder, of gap sensingtechniques, and of overlay mark detection systems, among other things.Exposure of the template may be performed: i) at normal incidences tothe template, ii) at inclined angles to the template, or iii) through aside surface of the template. In some embodiments, a template that isrigid may be used in combination with a flexible substrate.

The template may be manufactured using optical lithography, electronbeamlithography, ion-beam lithography, x-ray lithography, extremeultraviolet lithography, scanning probe lithography, focused ion beammilling, interferometric lithography, epitaxial growth, thin filmdeposition, chemical etch, plasma etch, ion milling, reactive ion etchor a combination of the above. The template may be formed on a substratehaving a flat, parabolic, spherical, or other surface topography. Thetemplate may be used with a substrate having a flat, parabolic,spherical, or other surface topography. The substrate may contain apreviously patterned topography and/or a film stack of multiplematerials.

In an embodiment depicted in FIG. 4, a template may include a patterningregion 401, an entrainment channel 402, and an edge 403. Template edge403 may be utilized for holding the template within a template holder.Entrainment channel 402 may be configured to entrain excess fluidthereby preventing its spread to adjacent patterning areas, as discussedin more detail below. In some embodiments, a patterned region of atemplate may be flat. Such embodiments may be useful for planarizing asubstrate.

In some embodiments, the template may be manufactured with a multi-depthdesign. That is various features of the template may be at differentdepths with relation to the surface of the template. For example,entrainment channel 402 may have a depth greater than patterning area401. An advantage of such an embodiment may be that accuracy in sensingthe gap between the template and substrate may be improved. Very smallgaps (e.g., less than about 100 nm) may be difficult to sense;therefore, adding a step of a known depth to the template may enablemore accurate gap sensing. An advantage of a dual-depth design may bethat such a design may enable using a standardized template holder tohold an imprint template of a given size which may include dies ofvarious sizes. A third advantage of a dual-depth design may enable usingthe peripheral region to hold the template. In such a system, allportions of the template and substrate interface having functionalstructures may be exposed to the curing agent. As depicted in FIG. 5, atemplate 500 with the depth of the peripheral region 501 properlydesigned may abut adjacent imprints 502, 503. Additionally, theperipheral region 501 of imprint template 500 may remain a safe verticaldistance away from imprints 503.

A dual-depth imprint template, as described above, may be fabricatedusing various methods. In an embodiment depicted in FIG. 6, a single,thick substrate 601 may be formed with both a high-resolution,shallow-depth die pattern 602, and a low-resolution, large-depthperipheral pattern 603. In an embodiment, as depicted in FIG. 7, a thinsubstrate 702 (e.g., quartz wafer) may be formed having ahigh-resolution, shallow-depth die pattern 701. Die pattern 701 may thenbe cut from substrate 702. Die pattern 701 may then be bonded to athicker substrate 703, which has been sized to fit into an imprinttemplate holder on an imprint machine. This bonding may be preferablyachieved using an adhesive 704 with an index of refraction of the curingagent (e.g., UV light) similar to that of the template material.

Additional imprint template designs are depicted in FIGS. 8A, 8B, and 8Cand generally referenced by numerals 801, 802, and 803, respectively.Each of template designs 801, 802 and 803 may include recessed regionswhich may be used for gap measurement and or entrainment of excessfluid.

In an embodiment, a template may include a mechanism for controllingfluid spread that is based on the physical properties of the materialsas well as geometry of the template. The amount of excess fluid whichmay be tolerated without causing loss of substrate area may limited bythe surface energies of the various materials, the fluid density andtemplate geometry. Accordingly, a relief structure may be used toentrain the excess fluid encompassing a region surrounding the desiredmolding or patterning area. This region may generally be referred to asthe “kerf.” The relief structure in the kerf may be recessed into thetemplate surface using standard processing techniques used to constructthe pattern or mold relief structure, as discussed above.

In conventional photolithography, the use of optical proximitycorrections in the photomasks design is becoming the standard to produceaccurate patterns of the designed dimensions. Similar concepts may beapplied to micro- and nano-molding or imprint lithography. A substantialdifference in imprint lithography processes may be that errors may notbe due to diffraction or optical interference but rather due to physicalproperty changes that may occur during processing. These changes maydetermine the nature or the need for engineered relief corrections inthe geometry of the template. A template in which a pattern reliefstructure is designed to accommodate material changes (such as shrinkageor expansion) during imprinting, similar in concept to optical proximitycorrection used in optical lithography, may eliminate errors due tothese changes in physical properties. By accounting for changes inphysical properties, such as volumetric expansion or contraction, reliefstructure may be adjusted to generate the exact desired replicatedfeature. For example, FIG. 9 depicts an example of an imprint formedwithout accounting for material property changes 901, and an imprintformed accounting for changes in material properties 902. In certainembodiments, a template with features having a substantially rectangularprofile 904, may be subject to deformations due to material shrinkageduring curing. To compensate for such material shrinkage, templatefeatures may be provided with an angled profile 905.

With respect to imprint lithography processes, the durability of thetemplate and its release characteristics may be of concern. A durabletemplate may be formed of a silicon or silicon dioxide substrate. Othersuitable materials may include, but are not limited to: silicongermanium carbon, gallium nitride, silicon germanium, sapphire, galliumarsinide, epitaxial silicon, poly-silicon, gate oxide, quartz orcombinations thereof. Templates may also include materials used to formdetectable features, such as alignment markings. For example, detectablefeatures may be formed of SiOx, where x is less than 2. In someembodiments x may be about 1.5. It is believed that this material may beopaque to visible light, but transparent to some activating lightwavelengths.

It has been found through experimentation that the durability of thetemplate may be improved by treating the template to form a thin layeron the surface of the template. For example, an alkylsilane, afluoroalkylsilane, or a fluoroalkyltrichlorosilane layer may be formedon the surface, in particular tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (C₅F₁₃C₂H₄SiCl₃) may be used. Such a treatment may forma self-assembled monolayer (SAM) on the surface of the template.

A surface treatment process may be optimized to yield low surface energycoatings. Such a coating may be used in preparing imprint templates forimprint lithography. Treated templates may have desirable releasecharacteristics relative to untreated templates. For example,newly-treated templates may posses surface free energies, λ_(treated) ofabout 14 dynes/cm. Untreated template surfaces may posses surface freeenergies, λ_(untreated) about 65 dynes/cm. A treatment proceduredisclosed herein may yield films exhibiting a high level of durability.Durability may be highly desirable since it may lead to a template thatmay withstand numerous imprints in a manufacturing setting.

A coating for the template surface may be formed using either aliquid-phase process or a vapor-phase process. In a liquid-phaseprocess, the substrate may be immersed in a solution of precursor andsolvent. In a vapor-phase process, a precursor may be delivered via aninert carrier gas. It may be difficult to obtain a purely anhydroussolvent for use in a liquid-phase treatments. Water in the bulk phaseduring treatment may result in clump deposition, which may adverselyaffect the final quality or coverage of the coating. In an embodiment ofa vapor-phase process, the template may be placed in a vacuum chamber,after which the chamber may be cycle-purged to remove excess water. Someadsorbed water may remain on the surface of the template. A small amountof water may be needed to complete a surface reaction which forms thecoating. It is believed that the reaction may be described by theformula:R−SiCl3+3H2O=>R−Si(OH)3+3HClTo facilitate the reaction, the template may be brought to a desiredreaction temperature via a temperature-controlled chuck. The precursormay then be fed into the reaction chamber for a prescribed time.Reaction parameters such as template temperature, precursorconcentration, flow geometries, etc. may be tailored to the specificprecursor and template substrate combination.

As previously mentioned, substance 40 may be a liquid so that it mayfill the space of gap 31. For example, substance 40 may be a lowviscosity liquid monomer solution. A suitable solution may have aviscosity ranging from about 0.01 cps to about 100 cps (measured at 25degrees C.). Low viscosities are especially desirable forhigh-resolution (e.g., sub-100 nm) structures. Low viscosities may alsolead to faster gap closing. Additionally, low viscosities may result infaster liquid filling of the gap area at low pressures. In particular,in the sub-50 nm regime, the viscosity of the solution should be at orbelow about 25 cps, or more preferably below about 5 cps (measured at 25degrees C.). In an embodiment, a suitable solution may include a mixtureof 50% by weight n-butyl acrylate and 50% SIA 0210.0(3-acryoloxypropyltristrimethylsiloxane)silane. To this solution may beadded a small percentage of a polymerization initiator (e.g., aphotoinitiator). For example, a 3% by weight solution of a 1:1 kg 819and kg 184 and 5% of SIB 1402.0 may be suitable. The viscosity of thismixture is about 1 cps.

In an embodiment, an imprint lithography system may include automaticfluid dispensing method and system for dispensing fluid on the surfaceof a substrate (e.g., a semiconductor wafer). The dispensing method mayuse a modular automated fluid dispenser with one or more extendeddispenser tips. The dispensing method may use an X-Y stage to generaterelative lateral motions between the dispenser tip and the substrate.The method may eliminate several problems with imprint lithography usinglow viscosity fluids. For example, the method may eliminate air bubbletrapping and localized deformation of an imprinting area. Embodimentsmay also provide a way of achieving low imprinting pressures whilespreading the fluid across the entire gap between the imprintingtemplate and the substrate, without unnecessary wastage of excess fluid.

In an embodiment, a dispensed volume may typically be less than about130 nl (nano-liter) for a 1 inch² imprint area. After dispensing,subsequent processes may involve exposing the template and substrateassembly to a curing agent. Separation of the template from thesubstrate may leave a transferred image on top of the imprinted surface.The transferred image may lie on a thin layer of remaining exposedmaterial. The remaining layer may be referred to as a “base layer.” Thebase layer should be thin and uniform for a manufacturable imprint. Athin and uniform base layer may assist in the break-through etch neededto eliminate the base layer while retaining the imprinted structure.

Imprint processes may involve high pressures and/or high temperaturesapplied at the template and substrate interface. However, for thepurpose of a manufacturable imprint lithography process including highresolution overlay alignment, high pressures and temperatures should beavoided. Embodiments disclosed herein avoid the need for hightemperature by using low viscosity photo-curable fluids. Further,imprinting pressures may be minimized by reducing squeezing forcerequired to spread the fluid across the entire imprinting area.Therefore, for the purpose of fluid based imprint lithography, a fluiddispense process should satisfy the following properties:

-   1. No air bubble should be trapped between template and substrate;-   2. Direct contact between the dispenser tip and substrate should be    avoided to minimize particle generation;-   3. Pressure required to fill the gap between template and substrate    in a timely manner should be minimized;-   4. Non-uniform fluid buildup and/or pressure gradients should be    minimized to reduce non-uniform localized deformation of    template-substrate interface; and-   5. Waste of the dispensed fluid should be minimized.

In some embodiments, relative motion between a displacement based fluiddispenser tip and a substrate may be used to form a pattern withsubstantially continuous lines on an imprinting area. Size of the crosssection of the line and the shape of the line may be controlled bybalancing rates of dispensing and relative motion. During the dispensingprocess, dispenser tips may be fixed near (e.g., on the order of tens ofmicrons) the substrate. Two methods of forming a line pattern aredepicted in FIGS. 10A and 10B. The pattern depicted in FIGS. 10A and 10Bis a sinusoidal pattern; however, other patterns are possible. Asdepicted in FIGS. 10A and 10B continue line pattern may be drawn usingeither a single dispenser tip 1001 or multiple dispenser tips 1002.

Dispensing rate, v_(d), and relative lateral velocity of a substrate,v_(s), may be related as follows:v _(d) =V _(d) /t _(d) (dispensing volume/dispensing period),  (1)v _(s) =L/t _(d) (line length/dispensing period),  (2)V_(d)=a L (where, ‘a’ is the cross section area of line pattern),  (3)Therefore,v_(d)=a v_(s).  (4)The width of the initial line pattern may normally depend on the tipsize of a dispenser. The tip dispenser may be fixed. In an embodiment, afluid dispensing controller 1111 (as depicted in FIG. 11) may be used tocontrol the volume of fluid dispensed (V_(d)) and the time taken todispense the fluid (t_(d)). If V_(d) and t_(d) are fixed, increasing thelength of the line leads to lower height of the cross section of theline patterned. Increasing pattern length may be achieved by increasingthe spatial frequency of the periodic patterns. Lower height of thepattern may lead to a decrease in the amount of fluid to be displacedduring imprint processes. By using multiple tips connected to the samedispensing line, line patterns with long lengths may be formed faster ascompared to the case of a single dispenser tip. In an embodiment, adisplacement based fluid delivery system may include: a fluid container1101, an inlet tube 1102, an inlet valve 1103, an outlet valve 1104, asyringe 1105, a syringe actuator 1106, a dispenser tip 1107, an X stageactuator 1109, a Y stage actuator 1110, a dispenser controller 1111, anXY stage controller 1112, and a main control computer 1113. A suitabledisplacement based dispenser may be available from the Hamilton Company.

FIG. 12 illustrates several undesirable fluid patterns or dispensingmethods for low viscosity fluids. These dispensing patterns may lead toone or more problems, including: trapping air bubbles, localizeddeformations, and waste of fluid. For example, dispensing a single dropat the center of the imprinting area 1201, or dispensing irregular lines1205 may lead to localized deformations of the template and/orsubstrate. Dispensing several drops 1202, or lines 1206 in acircumferential pattern may lead to trapping of air bubbles. Otherdispensing patterns with nearly closed circumferential patterns 1204 maysimilarly lead to air bubble trapping. Likewise, spraying or randomplacement of droplets 1203 may lead to trapping of air bubbles.Spin-coating a substrate with a low viscosity fluid may cause a“dewetting” problem due to the thin film instability. Dewetting may leadto formation of numerous small drops of fluid on the substrate, insteadof a thin uniform layer of fluid.

In an embodiment, a fluid dispensing method may dispense multiple smalldrops of liquid that may later be formed into a continuous body as theyexpand. FIGS. 13 depicts the case of using five drops of liquid. Here,five drops are used only for the purpose of illustration. Othernon-bubble forming patterns, such as a sinusoidal line, a ‘W’, or an ‘X’may be implemented using this method. As the template-substrate gapdecreases, circular drops 1301 may become thinner and wider causingneighboring drops to merge together 1302. Therefore, even though theinitial dispensing may not include a continuous form, the expandingliquid may expel air from the gap between the template and substrate. Apattern effective for use in this method should be dispensed in such away that as droplets expand, they do not trap any air between thetemplate and substrate.

Small drops of liquid whose volume may be accurately specified may bedispensed using micro-solenoid valves with a pressure-supporting unit.Another type of the liquid dispensing actuator may include apiezo-actuated dispenser. Advantages of a system with a micro-solenoidvalves dispenser as compared to a displacement based fluid dispenser mayinclude faster dispensing time and more accurate volume control. Theseadvantages may be especially desirable for larger size imprints (e.g.,several inches across). An embodiment of a system includingmicro-solenoid valves is depicted in FIG. 14. The system may include:fluid container 1401, an inlet tube 1402, an inlet valve 1403, a pump1404, an outlet valve 1405, a pump controller 1406, a micro-solenoidvalve 1407, a micro-solenoid valve controller 1408, an X-Y stage 1409,an X-Y stage controller 1410, and a main computer 1412. A substrate 1411may be placed on X-Y stage 1409. A suitable micro-valve dispenser systemmay be available from the Lee Company.

A dispensing pattern that may be useful for large imprint areas (e.g.,greater than several inch²) is depicted in FIG. 15A. In such anembodiment, parallel lines of fluid 1503 may be dispensed. Parallellines of fluid 1503 may be expanded in such a way that air may beexpelled from the gap as template 1501 approach substrate 1502. Tofacilitate expanding lines 1503 in the desired manner, template 1501 maybe close the gap in an intentionally wedged configuration (as depictedin FIG. 15B). That is, the template/substrate gap may be closed alonglines 1503 (e.g., the wedge angle may be parallel to the lines 1503).

An advantage of providing a well-distributed initial fluid layer may bethat the orientation error between the template and substrate may becompensated for. This may be due to the hydraulic dynamics of the thinlayer of fluid and compliance of the orientation stage. The lowerportion of the template may contact the dispensed fluid earlier thanother portions of the template. As the gap between the template andsubstrate gets smaller, the imbalance of reaction forces between thelower and higher portions of the template increases. This imbalance offorces may lead to a correcting motion for the template and substrate,bring them into a substantially parallel relationship.

Successful imprint lithography may require precise alignment andorientation of the template with respect to the substrate to control thegap in between the template and substrate. Embodiments presented hereinmay provide a system capable of achieving precise alignment and gapcontrol in a production fabrication process. In an embodiment, thesystem may include a high resolution X-Y translation stage. In anembodiment, the system may provide a pre-calibration stage forperforming a preliminary and course alignment operation between thetemplate and substrate surface to bring the relative alignment to withinthe motion range of a fine movement orientation stage. Thispre-calibration stage may be required only when a new template isinstalled into the apparatus (also sometimes known as a stepper). Thepre-calibration stage may consist of a base plate, a flexure component,and a plurality of micrometers or high resolution actuators coupling thebase plate and the flexure component.

FIG. 16 depicts an embodiment of an X-Y translation stage in anassembled configuration, and generally referenced by numeral 1600. Theoverall footprint may be less than about 20 inches by 20 inches and theheight may be about 6 inches (including a wafer chuck). Such anembodiment may provide X and Y-axis translation ranges of motion ofabout 12 inches.

A second embodiment of an X-Y translation stage is depicted in FIG. 17,and generally referenced by numeral 1700. To provide a similar range ofmotion to that of X-Y stage 1600, stage 1700 may have a foot print ofabout 29 inches by 29 inches and a height of about 15 inches (includinga wafer chuck). Stages 1600 and 1700 differ mainly in that additionallinkages 1701 are oriented vertically.

Both X-Y stage 1600 and X-Y stage 1700 are flexure based systems.Flexures are widely used in precision machines since they may offerfrictionless, particle-free and low maintenance operation. Flexures mayalso provide extremely high resolution. Examples of flexure basedsystems are disclosed in U.S. Pat. No. 4,694,703 to Routson and U.S.Pat. No. 4,062,600 to Wyse both of which are incorporated by referenceas if full set forth herein. However, most flexure based systems maypossess limited ranges of motion (e.g., sub mm range of motion).Embodiments disclosed herein may have a range of motion of more than 12inches. It is believed that such stages may be cost-effective forlithographic applications, particularly in vacuum. Further, for imprintlithography techniques, the presence of imprint forces may giveembodiments presented herein significant advantages.

In general, an X-Y stage may include two types of components: actuationcomponents and load-carrying components. Lead screw assembly mechanismshave been widely used where the positioning accuracy is not a verysignificant factor. For high accuracy applications, ball screwassemblies have been used for both the actuating and load-carryingcomponents. Both of these designs may be prone to problems of backlashand stiction. Further, the need for lubrication may make these designsundesirable for use in vacuum or in particle-sensitive applications(e.g., imprint lithography).

Additionally, some designs may utilize air bearings. Air bearings maysubstantially eliminate problems of stiction and backlash. However, airbearings may provide limited load bearing capacities. Additionally, airbearings may be unsuitable for use in vacuum environments.

FIG. 18 shows a schematic of portion of a basic linkage 1800. Link 1(1804) and link 3 (1805) may be of the same length. When a moving body1801 moves along the X-axis, all of the joints in linkage 1800 rotate bythe same absolute angle. It should be noted that the motion range may beindependent of the length of link 2 (1803). Due to kinematicconstraints, link 2 (1803) may remain parallel to a line between joint 1(1806) and joint 4 (1807). In linkage 1800, the range of motion, l_(m),may be given as: $\quad\begin{matrix}\begin{matrix}{l_{m} = {2\quad{d_{1}\left\lbrack {{\cos\left( {\theta_{0} - {\alpha_{\max}/2}} \right)} - {\cos\left( {\theta_{0} - {\alpha_{\max}/2}} \right)}} \right\rbrack}}} \\{{= {4\quad d_{1}{\sin\left( \theta_{0} \right)}{\sin\left( {\alpha_{\max}/2} \right)}}},}\end{matrix} & (5)\end{matrix}$

where, θ₀ is the angle of joint 1 (1806) when all flexure joints are intheir equilibrium conditions, α_(max) is the maximum rotation range ofthe flexure pivots, and d₁ is the length of links 1 and 3, 1804 and1805. As shown in Eqn. (5), for given d₁, the motion range is maximizedwhen θ₀=90 Degree. Therefore, the link length may be given as:d ₁ =l _(m)/[4 sin(α_(max)/2)]  (6)Therefore, using an α_(max) of 60°, the minimum link length for a 12inch motion range, is 6 inches.

FIG. 19 depicts an embodiment of a basic linkage similar to linkage1800, but with the addition of two cylindrical disks 1902. A kinematicstudy shows that if joint 2 1904 and joint 3 1905 of FIG. 19 rotate inopposite directions by the same angle, the stage may generate, a puretranslational motion along the X axis. By adding cylindrical disks 1902at flexure joints 2 1904 and 3 1905, the resulting rolling contact mayrotate link 11908 and link 2 1906 in opposite directions. In anembodiment, no additional joints or bearings may be required sincecylindrical discs 1902 may be coupled to links 1908 and 1906. In orderto prevent discs 1902 from slipping, an appropriate pre-load may beapplied between the two disks. Compared to conventional stages wheredirect driven mechanisms or bearings may be used, the contact surfacehere may be relatively small, and relatively easy to maintain. Note thatalthough disks 1902 are not depicted in relation to X-Y stages 1600, and1700, disks 1902 may be present in some embodiments. Links 1602 and 1601in FIG. 16 may correspond to links 1908 and 1906 of FIG. 19. Thus, disks1902 may be present at location 1603 (as well as other locations notvisible in the FIG. 16). Referring to FIG. 17, disks 1902 may be presentat location 1702 (as well as other locations not visible in FIG. 17).

As the actuation system for either of stages 1600 or 1700, two linearservo motors (as depicted in FIG. 20 and referenced by numeral 2000) maybe suitable. One linear servo motor may serve each translation axis.Suitable linear servo motors may be available from the Trilogy SystemsCorporation. An advantage of such linear servo motors may be the absenceof frictional contact. Another advantage of such linear servo motors maybe the fact that they may readily produce actuation forces greater thanabout 100 pounds. Therefore, actuation components may provide onlytranslational motion control in the X and Y directions. It should benoted that in some embodiments, the actuator of the lower stage mightneed to be more powerful than the actuator of the upper stage. In someembodiments, laser interferometers may provide a feedback signal tocontrol X and Y positioning of the X-Y stage. It is believed that laserinterferometry may provide nm level positioning control.

Placement errors can be compensated using laser interferometers and highresolution X-Y stages (such as X-Y stage 1700, depicted in FIG. 17). Ifthe orientation alignments between the template and substrate areindependent from X-Y motions the placement error may need to becompensated only once for an entire substrate wafer (i.e., “globaloverlay”). If orientation alignments between the template and substrateare coupled with X-Y motions and/or excessive local orientationvariations on substrate exist, then X-Y position changes of the templaterelative to the substrate may need to be compensated for (i.e.,field-to-field overlay). Overlay alignment issues are further discussedwith regard the overlay alignment section. FIGS. 21 and 22 provideglobal and field-to-field overlay error compensation algorithms,respectively.

-   -   In an embodiment, orientation of template and substrate may be        achieved by a pre-calibration stage (automatically, using        actuators or manual, using micrometers) and a fine orientation        stage, which may be active or passive. Either or both of these        stages may include other mechanisms, but flexure-based        mechanisms may be preferred in order to avoid particles. The        calibration stage may be mounted to a frame, and the fine        orientation stage may be mounted to the pre-calibration stage.        Such an embodiment may thereby form a serial mechanical        arrangement.    -   A fine orientation stage may include one or more passive        compliant members. A “passive compliant member” may generally        refer to a member that gets its motion from compliance.        Compliant members apparatus are disclosed in U.S. Pat. No.        4,414,750 to De Fazio; U.S. Pat. No. 4,337,579 to De Fazio; U.S.        Pat. No. 4,155,169 to Drake et al.; U.S. Pat. No. 4,355,469 to        Nevins et al.; U.S. Pat. No. 4,202,107 to Watson; and U.S. Pat.        No. 4,098,001 to Watson; each of which are incorporated by        reference as if fully set forth herein. That is, motion may be        activated by direct or indirect contact with the liquid. If the        fine orientation stage is passive, then it may be designed to        have the most dominant compliance about two orientation axes.        The two orientation axes may be orthogonal and may lie on the        template lower surface (as described with referenced to FIG.        43). The two orthogonal torsional compliance values may        typically be the same for a square template. The fine        orientation stage may be designed such that when the template is        non-parallel with respect to the substrate, as it makes contact        with the liquid, the resulting uneven liquid pressure may        rapidly correct the orientation error. In an embodiment, the        correction may be affected with minimal, or no overshoot.        Further, a fine orientation stage as described above may hold        the substantially parallel orientation between the template and        substrate for a sufficiently long period to allow curing of the        liquid.

In an embodiment, a fine orientation stage may include one or moreactuators. For example, piezo actuators (as described with reference toFIG. 46) may be suitable. In such an embodiment, the effective passivecompliance of the fine orientation stage coupled with thepre-calibration stage should still be substantially about the twoorientation axes. The geometric and material parameters of all thestructural and active elements together may contribute to this effectivepassive stiffness. For instance, piezo actuators may also be compliantin tension and compression. The geometric and material parameters may besynthesized to obtain the desired torsional compliance about the twoorientation axes. A simple approach to this synthesis may be to make thecompliance of the actuators along their actuation direction in the fineorientation stage higher than the structural compliances in the rest ofthe stage system. This may provide passive self-correction capabilitywhen a non-parallel template comes into contact with the liquid on thesubstrate. Further, this compliance should be chosen to allow forrapidly correcting orientation errors, with minimal or no overshoot. Thefine orientation stage may hold the substantially parallel orientationbetween the template and substrate for sufficiently long period to allowcuring of the liquid.

Overlay alignment schemes may include measurement of alignment errorsfollowed by compensation of these errors to achieve accurate alignmentof an imprint template, and a desired imprint location on a substrate.The measurement techniques used in proximity lithography, x-raylithography, and photolithography (e.g., laser interferometry,capacitance sensing, automated image processing of overlay marks on themask and substrate, etc.) may be adapted for the imprint lithographyprocess with appropriate modifications. A method and system of overlayalignment using a stored image is disclosed in U.S. Pat. No. 5,204,739,which is incorporated by reference as if fully set forth herein.

Types of overlay errors for lithography processes may include placementerror, theta error, magnification error, and mask distortion error. Anadvantage of embodiments disclosed herein may be that mask distortionerrors may not be present because the disclosed processes may operate atrelatively low temperatures (e.g., room temperature) and low pressures.Therefore, these embodiments may not induce significant distortion.Further, these embodiments may use templates that are made of arelatively thick substrate. This may lead to much smaller mask (ortemplate) distortion errors as compared to other lithography processeswhere masks are made of relatively thin substrates. Further, the entirearea of the templates for imprint lithography processes may betransparent to the curing agent (e.g., UV light), which may minimizeheating due to absorption of energy from the curing agent. The reducedheating may minimize the occurrence of heat-induced distortions comparedto photolithography processes where a significant portion of the bottomsurface of a mask may be opaque due to the presence of a metalliccoating.

Placement error may generally refer to X-Y positioning errors between atemplate and substrate (that is, translation along the X and/or Y-axis).Theta error may generally refer to the relative orientation error aboutZ-axis (that is, rotation about the Z-axis). Magnification error maygenerally refer to thermal, optical or material induced shrinkage orexpansion of the imprinted area as compared to the original patternedarea on the template.

In imprint lithography processes, orientation alignment for gap controlpurposes between a template and substrate corresponding to the angles αand β in FIG. 23 may need to be performed frequently if excessivefield-to-field surface variations exist on the substrate. In general, itis desirable for the variation across an imprinting area to be smallerthan about one-half of the imprinted feature height. If orientationalignments are coupled with the X-Y positioning of the template andsubstrate, field-to-field placement error compensations may benecessary. However, embodiments of orientation stages that may performorientation alignment without inducing placement errors are presentedherein.

Photolithography processes that use a focusing lens system may positionthe mask and substrate such that it may be possible to locate the imagesof two alignment marks (one on the mask and the other on the substrate)onto the same focal plane. Alignment errors may be induced by looking atthe relative positioning of these alignment marks. In imprintlithography processes, the template and substrate maintain a relativelysmall gap (of the order of micro meters or less) during the overlayerror measurement. Therefore, overlay error measurement tools may needto focus two overlay marks from different planes onto the same focalplane. Such a requirement may not be critical for devices with featuresthat are relatively large (e.g., about 0.5 μm). However, for criticalfeatures in the sub-100 nm region, the images of the two overlay marksshould to be captured on the same focal plane in order to achieve highresolution overlay error measurements.

Accordingly, overlay error measurement and error compensation methodsfor imprint lithography processes should to satisfy the followingrequirements:

-   -   1. Overlay error measurement tools should be able to focus on        two overlay marks that are not on the same plane;    -   2. Overlay error correction tools should be able to move the        template and substrate relatively in X and Y in the presence of        a thin layer of fluid between the template and substrate;    -   3. Overlay error correction tools should be able to compensate        for theta error in the presence of a thin layer of fluid between        the template and substrate; and    -   4. Overlay error correction tools should be able to compensate        for magnification error.

The first requirement presented above can be satisfied by i) moving anoptical imaging tool up and down (as in U.S. Pat. No. 5,204,739) or ii)using illumination sources with two different wavelengths. For boththese approaches, knowledge of the gap measurement between the templateand the substrate is useful, especially for the second method. The gapbetween the template and substrate may be measured using one of existingnon-contact film thickness measurement tools including broad-bandinterferometry, laser interferometry and capacitance sensors.

FIG. 24 illustrates the positions of template 2400, substrate 2401,fluid 2403, gap 2405 and overlay error measurement tools 2402. Theheight of a measuring tool may be adjusted 2406 according to the gapinformation to acquire two overlay marks on the same imaging plane. Inorder to fulfill this approach an image storing 2407 device may berequired. Additionally, the positioning devices of the template andwafer should be vibrationally isolated from the up and down motions ofthe measuring device 2402. Further, when scanning motions in X-Ydirections between the template and substrate are needed for highresolution overlay alignment, this approach may not produce continuousimages of the overlay marks. Therefore, this approach may be adapted forrelatively low-resolution overlay alignment schemes for the imprintlithography process.

FIG. 25 illustrates an apparatus for focusing two alignment marks fromdifferent planes onto a single focal plane. Apparatus 2500 may use thechange of focal length resulting from light with distinct wavelengthsbeing used as the illumination sources. Apparatus 2500 may include animage storage device 2503, and illumination source (not shown), and afocusing device 2505. Light with distinct wavelengths may be generatedeither by using individual light sources or by using a single broad bandlight source and inserting optical band-pass filters between the imagingplane and the alignment marks. Depending on the gap between the template2501 and substrate 2502, a different set of two wavelengths may beselected to adjust the focal lengths. Under each illumination, eachoverlay mark may produce two images on the imaging plane as depicted inFIG. 26. A first image 2601 may be a clearly focused image. A secondimage 2602 may be an out-of-focus image. In order to eliminate eachout-of-focus image, several methods may be used.

In a first method, under illumination with a first wavelength of light,two images may be received by an imaging array (e.g., a CCD array).Images which may be received are depicted in FIG. 26 and generallyreferenced by numeral 2604. Image 2602 may correspond to an overlayalignment mark on the substrate. Image 2601 may correspond to an overlayalignment mark on the template. When image 2602 is focused, image 2601may be out of focus, and visa-versa. In an embodiment, an imageprocessing technique may be used to erase geometric data correspondingto pixels associated with image 2602. Thus, the out of focus image ofthe substrate mark may be eliminated, leaving image 2601. Using the sameprocedure and a second wavelength of light, image 2605 and 2606 may beformed on the imaging array. The procedure may eliminate out of focusimage 2606. Thus image 2605 may remain. The two remaining focused images2601 and 2605 may then be combined onto a single imaging plane 2603 formaking overlay error measurements.

A second method may utilize two coplanar polarizing arrays, as depictedin FIG. 27, and polarized illumination sources. FIG. 27 illustratesoverlay marks 2701 and orthogonally polarized arrays 2702. Polarizingarrays 2702 may be made on the template surface or may be placed aboveit. Under two polarized illumination sources, only focused images 2703(each corresponding to a distinct wavelength and polarization) mayappear on the imaging plane. Thus, out of focus images may be filteredout by polarizing arrays 2702. An advantage of this method may be thatit may not require an image processing technique to eliminateout-focused images.

It should be noted that, if the gap between the template and substrateis too small during overlay measurement, error correction may becomedifficult due to stiction or increased shear forces of the thin fluidlayer. Additionally, overlay errors may be caused by the non-idealvertical motion between the template and substrate if the gap is toolarge. Therefore, an optimal gap between the template and substrateshould to be determined, where the overlay error measurements andcorrections may be performed.

Moire pattern based overlay measurement has been used for opticallithography processes. For imprint lithography processes, where twolayers of Moire patterns are not on the same plane but still overlappedin the imaging array, acquiring two individual focused images may bedifficult to achieve. However, carefully controlling the gap between thetemplate and substrate within the depth of focus of the opticalmeasurement tool and without direct contact between the template andsubstrate may allow two layers of Moire patterns to be simultaneouslyacquired with minimal focusing problems. It is believed that otherstandard overlay schemes based on the Moire patterns may be directlyimplemented to imprint lithography process.

Placement errors may be compensated for using capacitance sensors orlaser interferometers to locate the substrate on a high resolution X-Ystage, and high resolution motion of these X-Y stages. In an embodimentwhere orientation alignments between the template and substrate areindependent from X-Y motions, placement error may need to be compensatedfor only once for an entire substrate (e.g., a semiconductor wafer).Such a method may be referred to as a “global overlay.” If orientationalignments between the template and substrate are coupled with X-Ymotions and excessive local orientation variations exist on thesubstrate, X-Y position change of the template may be compensated forusing capacitance sensors and/or laser interferometers. Such a methodmay be referred to as a “field-to-field overlay.” FIGS. 28 and 29 depictsuitable sensor implementations. FIG. 28 depicts an embodiment of acapacitance sensing system. A capacitance sensing system may includecapacitance sensors 2801, a conductive coating 2802, on a template 2803.Thus, by sensing differences in capacitance, the location of template2803 may be determined. Similarly, FIG. 29 depicts an embodiment of alaser interferometer system including reflective coating 2901, lasersignal 2902, received 2903. Laser signals received by receiver 2903 maybe used to determine the location of template 2904.

The magnification error, if any exists, may be compensated for bycarefully controlling the temperature of the substrate and the template.Using the difference of the thermal expansion properties of thesubstrate and template, the size of pre-existing patterned areas on thesubstrate may be adjusted to that of a new template. However, it isbelieved that the magnification error may be much smaller in magnitudethan placement error or theta error when an imprint lithography processis conducted at room temperature and low pressures. Magnification errormay also be compensated for by using stress-based methods as disclosedherein.

The theta error may be compensated for using a theta stage that has beenwidely used for photolithography processes. Theta error may becompensated for by using two separate alignment marks that are separatedby a sufficiently large distance to provide a high resolution thetaerror estimate. The theta error may be compensated for when the templateis positioned a few microns or less apart from the substrate prior tocuring the liquid.

Another concern with overlay alignment for imprint lithography processesthat use UV curable liquid materials may be the visibility of thealignment marks. For the overlay error measurement, two overlay marks,one on the template and the other on substrate may be used. However,since it may be desirable for the template to be transparent to a curingagent, the template overlay marks may typically not include opaquelines. Rather, the template overlay marks may be topographical featuresof the template surface. In some embodiment, the marks may be made ofthe same material as the template. In addition, UV curable liquids maytend to have refractive indices that are similar to those of thetemplate materials (e.g., quartz). Therefore, when the UV curable liquidfills the gap between the template and the substrate, template overlaymarks may become very difficult to recognize. If the template overlaymarks are made with an opaque material (e.g., chromium), the UV curableliquid below the overlay marks may not be properly exposed to the UVlight, which is highly undesirable.

Two methods are disclosed to overcome the problem of recognizingtemplate overlay mark in the presence of the liquid. A first method usesan accurate liquid dispensing system along with high-resolution gapcontrolling stages. Suitable liquid dispensing systems and the gapcontrolling stages are disclosed herein. For the purpose ofillustration, three steps of an overlay alignment are depicted in FIG.30. The locations of the overlay marks and the patterns of the fluiddepicted in FIG. 30 are only for the purpose of illustration and shouldnot be construed in a limiting sense. Various other overlay marks,overlay mark locations, and/or liquid dispense patterns are alsopossible. First, in step 3001, a liquid 3003 may be dispensed ontosubstrate 3002. Then, in step 3004, using the high-resolutionorientation stage, the gap between template 3005 and substrate 3002 maybe carefully controlled so that the dispensed fluid 3003 does not fillthe gap between the template and substrate completely. It is believedthat at step 3004, the gap may be only slightly larger than the finalimprinting gap. Since most of the gap is filled with the fluid, overlaycorrection can be performed as if the gap were completely filled withthe fluid. The overlay marks may be placed such that the liquid does notcover them in this first position. Upon the completion of the overlaycorrection, the gap may be closed to a final imprinting gap (step 3006).This may enable spreading of the liquid into the remaining imprint area,including covering the alignment marks. Since the gap change betweensteps 3004 and 3006 may be very small (e.g., about 10 nm), the gapclosing motion is unlikely to cause any significant overlay error.

A second method may be to make special overlay marks on the templatethat may be seen by the overlay measurement tool but may not be opaqueto the curing agent (e.g., UV light). An embodiment of this approach isillustrated in FIG. 31. In FIG. 31, instead of completely opaque lines,overlay marks 3102 on the template may be formed of fine polarizinglines 3101. For example, suitable fine polarizing lines may have a widthabout ½ to ¼ of the wavelength of activating light used as the curingagent. The line width of polarizing lines 3101 should be small enough sothat activating light passing between two lines is diffractedsufficiently to cause curing of all the liquid below the lines. In suchan embodiment, the activating light may be polarized according to thepolarization of overlay marks 3102. Polarizing the activating light mayprovide a relatively uniform exposure to all the template regionsincluding regions having overlay marks 3102. Light used to locateoverlay marks 3102 on the template may be broadband light or a specificwavelength that may not cure the liquid material. This light need not bepolarized. Polarized lines 3101 may be substantially opaque to themeasuring light, thus making the overlay marks visible using establishedoverlay error measuring tools. Fine polarized overlay marks may befabricated on the template using existing techniques, such as electronbeam lithography.

In a third embodiment, overlay marks may be formed of a differentmaterial than the template. For example, a material selected to form thetemplate overlay marks may be substantially opaque to visible light, buttransparent to activating light used as the curing agent (e.g., UVlight). For example, SiOx where X is less than 2 may form such amaterial. In particular, it is believed that structures formed of SiOxwhere X is about 1.5 may be substantially opaque to visible light, buttransparent to UV light.

FIG. 32, depicts an assembly of a system, denoted generally as 100, forcalibrating and orienting a template, such as template 12, about asubstrate to be imprinted, such as substrate 20. System 100 may beutilized in a machine, such as a stepper, for mass fabrication ofdevices in a production environment using imprint lithography processesas described herein. As shown, system 100 may be mounted to a top frame110 which may provide support for a housing 120. Housing 120 may containthe pre calibration stage for course alignment of a template 150 about asubstrate (not shown in FIG. 32).

Housing 120 may be coupled to a middle frame 114 with guide shafts 112a, 112 b attached to middle frame 114 opposite housing 120. In oneembodiment, three (3) guide shafts may be used (the back guide shaft isnot visible in FIG. 32) to provide a support for housing 120 as itslides up and down during vertical translation of template 150. Sliders116 a and 116 b attached to corresponding guide shafts 112 a, 112 babout middle frame 114 may facilitate this up and down motion of housing120.

System 100 may include a disk-shaped base plate 122 attached to thebottom portion of housing 120. Base plate 122 may be coupled to adisk-shaped flexure ring 124. Flexure ring 124 may support the lowerplaced orientation stage included of first flexure member 126 and secondflexure member 128. The operation and configuration of the flexuremembers 126, 128 are discussed in detail below. As depicted in FIG. 33,the second flexure member 128 may include a template support 130, whichmay hold template 150 in place during the imprinting process. Typically,template 150 may include a piece of quartz with desired featuresimprinted on it. Template 150 may also include other substancesaccording to well-known methods.

As shown in FIG. 33, actuators 134 a, 134 b, 134 c may be fixed withinhousing 120 and operable coupled to base plate 122 and flexure ring 124.In operation, actuators 134 a, 134 b, 134 c may be controlled such thatmotion of the flexure ring 124 is achieved. Motion of the actuators mayallow for coarse pre-calibration. In some embodiments, actuators 134 a,134 b, 134 c may include high resolution actuators. In such embodiments,the actuators may be equally spaced around housing 120. Such anembodiment may permit very precise translation of the ring 124 in thevertical direction to control the gap accurately. Thus, the system 100may be capable of achieving coarse orientation alignment and precise gapcontrol of template 150 with respect to a substrate to be imprinted.

System 100 may include a mechanism that enables precise control oftemplate 150 so that precise orientation alignment may be achieved and auniform gap may be maintained by the template with respect to asubstrate surface. Additionally, system 100 may provide a way ofseparating template 150 from the surface of the substrate followingimprinting without shearing of features from the substrate surface.Precise alignment and gap control may be facilitated by theconfiguration of the first and second flexure members, 126 and 128,respectively.

In an embodiment, template 5102 may be held in place using a separated,fixed supporting plate 5101 that is transparent to the curing agent asdepicted in FIG. 51. While supporting plate 5101 behind template 5102may support the imprinting force, applying vacuum between fixedsupporting plate 5101 and template 5102 may support the separationforce. In order to support template 5102 for lateral forces, piezoactuators 5103 may be used. The lateral supporting forces may becarefully controlled by using piezo actuators 5103. This design may alsoprovide the magnification and distortion correction capability forlayer-to-layer alignment in imprint lithography processes. Distortioncorrection may be very important to overcome stitching and placementerrors present in the template structures made by electron beamlithography, and to compensate for distortion in the previous structurespresent on the substrate. Magnification correction may only require onepiezo actuator on each side of the template (i.e. total of 4 piezoactuators for a four sided template). The actuators may be connected tothe template surface in such a way that a uniform force may be appliedon the entire surface. Distortion correction, on the other hand, mayrequire several independent piezo actuators that may apply independentlycontrolled forces on each side of the template. Depending on the levelof distortion control required, the number of independent piezoactuators may be specified. More piezo actuators may provide bettercontrol of distortion. The magnification and distortion error correctionshould be completed prior to the use of vacuum to constrain the topsurface of the template. This is because magnification and distortioncorrection may be properly controlled only if both the top and bottomsurfaces of the template are unconstrained. In some embodiments, thetemplate holder system of FIG. 51 may have a mechanical design thatcauses obstruction of the curing agent to a portion of the area undertemplate 5102. This may be undesirable because a portion of the liquidbelow template 5102 may not cure. This liquid may stick to the templatecausing problems with further use of the template. This problem with thetemplate holder may be avoided by incorporating a set of mirrors intothe template holder to divert the obstructed curing agent in such a waythat curing agent directed to the region below one edge of template 5102may be bent to cure an obstructed portion below the other edge oftemplate 5102.

In an embodiment, high resolution gap sensing may be achieved bydesigning the template such that the minimum gap between the substrateand template falls within a sensing technique's usable range. The gapbeing measured may be manipulated independently of the actual patternedsurface. This may allow gap control to be performed within the usefulrange of the sensing technique. For example, if a spectral reflectivityanalysis technique with a useful sensing range of about 150 nm to 20microns is to be used to analyze the gap, then the template may havefeature patterned into the template with a depth of about 150 nm orgreater. This may ensure that the minimum gap that to be sensed isgreater than 150 nm.

As the template is lowered toward the substrate, the fluid may beexpelled from the gap between the substrate and the template. The gapbetween the substrate and the template may approach a lower practicallimit when the viscous forces approach equilibrium conditions with theapplied compressive force. This may occur when the surface of thetemplate is in close proximity to the substrate. For example, thisregime may be at a gap height of about 100 nm for a 1 cP fluid when 14kPa is applied for 1 sec to a template with a radius of 1 cm. As aresult, the gap may be self-limiting provided a uniform and parallel gapis maintained. Also, a fairly predictable amount of fluid may beexpelled (or entrained). The volume of fluid entrained may bepredictable based on careful fluid dynamic and surface phenomenacalculations.

For production-scale imprint patterning, it may be desired to controlthe inclination and gap of the template with respect to a substrate. Inorder to accomplish the orientation and gap control, a templatemanufactured with reticle fabrication techniques may be used incombination with gap sensing technology such as i) single wavelengthinterferometry, ii) multi-wavelength interferometry, iii) ellipsometry,iv) capacitance sensors, or v) pressure sensors.

In an embodiment, a method of detecting gap between template andsubstrate may be used in computing thickness of films on the substrate.A description of a technique based on Fast Fourier Transform (FFT) ofreflective data obtained from a broad-band spectrometer is disclosedherein. This technique may be used for measuring the gap between thetemplate and the substrate, as well as for measuring film thickness. Formulti-layer films, the technique may provide an average thickness ofeach thin film and its thickness variations. Also, the average gap andorientation information between two surfaces in close proximity, such asthe template-substrate for imprint lithography processes may be acquiredby measuring gaps at a minimum of three distinct points through one ofthe surfaces.

In an embodiment, a gap measurement process may be based the combinationof the broad-band interferometry and Fast Fourier Transform (FFT).Several applications in current industry utilized various curve fittingtechniques for the broad-band interferometry to measure a single layerfilm thickness. However, it is expected that such techniques may notprovide real time gap measurements, especially in the case ofmulti-layer films, for imprint lithography processes. In order toovercome such problems, first the reflective indexes may be digitized inwavenumber domain, between 1/λ_(high) and 1/λ_(low). Then, the digitizeddata may be processed using a FFT algorithm. This novel approach mayyield a clear peak of the FFT signal that accurately corresponds to themeasured gap. For the case of two layers, the FFT signal may yield twoclear peaks that are linearly related to the thickness of each layer.

For optical thin films, the oscillations in the reflectivity areperiodic in wavenumber (w) not wavelength (λ), such as shown in thereflectivity of a single optical thin film by the following equation,$\begin{matrix}{{R = \frac{\rho_{1,2}^{2} + {\rho_{2,3}^{2}{\mathbb{e}}^{{- 2}\alpha\quad d}} - {2\rho_{1,2}\rho_{2,3}{\mathbb{e}}^{{- \alpha}\quad d}{\cos\left( {4\pi\quad{{nd}/\lambda}} \right)}}}{1 - {\left( {\rho_{1,2}\rho_{2,3}} \right)^{2}{\mathbb{e}}^{{- 2}\alpha\quad d}} + {2\rho_{1,2}\rho_{2,3}{\mathbb{e}}^{{- \alpha}\quad d}{\cos\left( {4\pi\quad{{nd}/\lambda}} \right)}}}},} & (7)\end{matrix}$where ρ_(i,i+l) are the reflectivity coefficients at the interface ofthe i−l and i interface, n is the index of refraction, d is thethickness to measure of the film (material 2 of FIG. 52), and α is theabsorption coefficient of the film (material 2 of FIG. 52). Here, w=1/λ.

Due to this characteristic, Fourier analysis may be a useful techniqueto determine the period of the function R represented in terms of w. Itis noted that, for a single thin film, a clearly defined single peak(p₁) may result when a Fourier transform of R(w) is obtained. The filmthickness (d) may be a function of the location of this peak such as,

 d=p ₁/(Δw×2n),  (8)

where Δw=w_(f)−w_(s); w_(f)=1/λ_(min) and w_(s)=1/λ_(max).

FFT is an established technique in which the frequency of a discretesignal may be calculated in a computationally efficient way. Thus, thistechnique may be useful for in-situ analysis and real-time applications.FIG. 34 depicts an embodiment of a process flow of film thickness orgap, measurement via a FFT process of a reflectivity signal. Formulti-layer films with distinct reflective indexes, locations of peaksin FFT process may correspond to linear combinations of each filmthickness. For example, a two-layer film may lead to two distinct peaklocations in a FFT analysis. FIG. 35 depicts a method of determining thethickness of two films based on two peak locations.

Embodiments presented herein may enable measuring a gap or filmthickness even when the oscillation of the reflectivity data includesless than one full period within the measuring wavenumber range. In sucha case, FFT may result in an inaccurate peak location. In order toovercome such a problem and to extend the lower limit of the measurablefilm thickness, a novel method is disclosed herein. Instead of using aFFT algorithm to compute the period of the oscillation, an algorithm tofind a local minimum (w₁) or maximum point (w₂) of the reflectivitybetween w_(s) and w_(f) may be used to compute the period information:dR/dw=0 at w₁ and w₂. The reflectivity R(w) of Equation 7 has itsmaximum at w=0. Further, the wavenumber range (Δw) of typicalspectrometers may be larger than w_(s). For a spectrometer with 200nm-800 nm wavelength range, Δw=3/800 whereas w_(s)=1/800. Therefore, theoscillation length of the reflectivity data between 0-w_(s) may besmaller than that of Δw. As depicted in FIG. 36, there may be two casesof the locations of minimum and maximum in the Δw range, given that w=0is a maximum point of R(w). Therefore, the film thickness can becomputed as follows:

-   -   Case 1 WW0: a local minimum exists at w₁. Therefore, w₁=one half        of the periodic oscillation, and hence d=0.5/(w₁×2n).    -   Case 2 WW1: a local maximum exists at w₂. Therefore, w₂=one        period of the periodic oscillation, and hence d=1/(w₂×2n).

A practical configuration of the measurement tool may include abroad-band light source, a spectrometer with fiber optics, a dataacquisition board, and a processing computer. Several existing signalprocessing techniques may improve the sensitivity of the FFT data. Forexample, techniques including but not limited to: filtering,magnification, increased number of data points, different range ofwavelengths, etc., may be utilized with gap or film thicknessmeasurement methods disclosed herein.

Embodiments disclosed herein include a high precision gap andorientation measurement method between two flats (e.g., a template and asubstrate). Gap and orientation measurement methods presented hereinclude use of broad-band interferometry and fringe basedinterferometry. Methods and systems for gap sensing using interferometryare disclosed in U.S. Pat. No. 5,515,167 to Ledger et al.; U.S. Pat. No.6,204,922 to Chalmers; U.S. Pat. No. 6,128,085 to Buermann et al; andU.S. Pat. No. 6,091,485 to Li et al., all of which are incorporated byreference as if full set forth herein. In an embodiment, a methoddisclosed herein which uses broad-band interferometry may overcome adisadvantage of broad-band interferometer, namely its inability toaccurately measure gaps smaller than about ¼ of the mean wavelength ofthe broad-band signal. Interference fringe based interferometry may beused for sensing errors in the orientation of the template soon after itis installed.

Imprint lithography processes may be implemented to manufacture singleand multi layer devices. Single layer devices, such as micron sizeoptical mirrors, high resolution light filters, light guides may bemanufactured by forming a thin layer of material in certain geometricshapes on substrates. The imprinted layer thickness of some of thesedevices may be less than ¼ of the mean wavelength of a broad-bandsignal, and may be uniform across an active area. A disadvantage ofbroad-band interferometer may be that it may be unable to accuratelymeasure gaps smaller than about ¼ of the mean wavelength of thebroad-band signal (e.g., about 180 nm). In an embodiment, micrometersize steps, which may be measured accurately, may be etched into thesurface of the template. As depicted in FIG. 37, steps may be etcheddown in the forms of continuous lines 3701 or multiple isolated dots3702 where measurements may be made. Isolated dots 3702 may bepreferable from the point of view of maximizing the useful active areaon the template. When the patterned template surface is only a fewnanometers from the substrate, a broad-band interferometer may measurethe gap accurately without suffering from minimum gap measurementproblems.

FIG. 38 depicts a schematic of the gap measurement described here.Probes 3801 may also be used in an inclined configuration, such asdepicted in FIG. 39. If more than three probes are used, the gapmeasurement accuracy may be improved by using the redundant information.For simplicity's sake, the ensuing description assumes the use of threeprobes. The step size, h_(s), is magnified for the purpose ofillustration. The average gap at the patterned area, h_(p), may be givenas:h _(p)=[(h ₁ +h ₂ +h ₃)/3]−h _(s),  (9)When the positions of the probes are known ((x_(i), y_(i)), where x andy axes are on the substrate surface), the relative orientation of thetemplate with respect to the substrate may be expressed as an unitvector (n) that is normal to the template surface with respect to aframe whose x-y axes lie on the top surface of the substrate.n=r/∥r∥,  (10)where, r=[(x₃, y₃, h₃)−(x₁, y₁, h₁)]×[(x₂, y₂, h₂)−(x₁, y₁, h₁)].Perfect orientation alignment between two flats may be achieved whenn=(0 0 1)^(T), or h₁=h₂=h₃.

Measured gaps and orientations may be used as feedback information toimprinting actuators. The size of the measuring broad-bandinterferometric beam may be as small as about 75 μm. For a practicalimprint lithography process, it may be desirable to minimize the cleararea used only to measure the gap since no pattern can be etched intothe clear area. Further, blockage of the curing agent due to thepresence of measurement tool should be minimized.

FIG. 40 depicts a schematic of multi-layer materials on substrates. Forexample, substrate 4001 has layers 4002, and 4003, and fluid 4005between substrate 4001 and template 4004. These material layers may beused to transfer multiple patterns, one by one vertically, onto thesubstrate surface. Each thickness may be uniform at the clear area wherea gap measurement may be made using light beams 4006. It has been shownthat using broad-band interferometry, the thickness of a top layer maybe measured accurately in the presence of multi-layer films. When theoptical properties and thicknesses of lower layer films are knownaccurately, the gap and orientation information between the template andsubstrate surface (or metal deposited surfaces for multi-layer devices)may be obtained by measuring the top layer thickness. The thickness ofeach layer may be measured using the same sensing measurement probes.

It may be necessary to perform orientation measurement and correspondingcalibration when a new template is installed or a machine component isreconfigured. The orientation error between the template 4102 andsubstrate 4103 may be measured via an interference fringe pattern at thetemplate and substrate interface as depicted in FIG. 41. For two opticalflats, the interference fringe pattern may appear as parallel dark andlight bands 4101. Orientation calibration may be performed using apre-calibration stage as disclosed herein. Differential micrometers maybe used to adjust the relative orientation of the template with respectto the substrate surface. Using this approach, if no interference fringeband is present, the orientation error may be corrected to be less than¼ of the wavelength of light source used.

With reference to FIGS. 42A and 42B, therein are depicted embodiments ofthe first and second flexure members, 126 and 128, respectively, in moredetail. Specifically, the first flexure member 126 may include aplurality of flexure joints 160 coupled to corresponding rigid bodies164, 166. Flexure joints 160 and rigid bodies 164, and 166 may form partof arms 172, 174 extending from a frame 170. Flexure frame 170 may havean opening 182, which may permit the penetration of a curing agent(e.g., UV light) and a sensing agent (e.g., for gap sensing and/oroverlay alignment sensing) to reach the template 150 when held insupport 130. In some embodiments, four (4) flexure joints 160 mayprovide motion of the flexure member 126 about a first orientation axis180. Frame 170 of first flexure member 126 may provide a couplingmechanism for joining with second flexure member 128 as illustrated inFIG. 43.

Likewise, second flexure member 128 may include a pair of arms 202, 204extending from a frame 206. Arms 202 and 204 may include flexure joints162 and corresponding rigid bodies 208, 210. Rigid bodies 208 and 210may be adapted to cause motion of flexure member 128 about a secondorientation axis 200. A template support 130 may be integrated withframe 206 of the second flexure member 128. Like frame 182, frame 206may have an opening 212 permitting a curing agent and a sensing agent toreach template 150 which may be held by support 130.

In operation, first flexure member 126 and second flexure member 128 maybe joined as shown in FIG. 43 to form orientation stage 250. Braces 220,222 may be provided in order to facilitate joining of the two piecessuch that the first orientation axis 180 and second orientation axis 200are substantially orthogonal to each other. In such a configuration,first orientation axis 180 and second orientation may intersect at apivot point 252 at approximately the template substrate interface 254.The fact that first orientation axis 180 and second orientation axis 200are orthogonal and lie on interface 254 may provide fine alignment andgap control. Specifically, with this arrangement, a decoupling oforientation alignment from layer-to-layer overlay alignment may beachieved. Furthermore, as explained below, the relative position offirst orientation axis 180 and second orientation axis 200 may providean orientation stage 250 that may be used to separate the template 150from a substrate without shearing of desired features. Thus, featurestransferred from the template 150 may remain intact on the substrate.

Referring to FIGS. 42A, 42B and 43, flexure joints 160 and 162 may benotched shaped to provide motion of rigid bodies 164, 166, 208, 210about pivot axes that are located along the thinnest cross section ofthe notches. This configuration may provide two (2) flexure-basedsub-systems for a fine decoupled orientation stage 250 having decoupledcompliant motion axes 180, 200. Flexure members 126, 128 may beassembled via mating of surfaces such that motion of template 150 mayoccur about pivot point 252 substantially eliminating “swinging” andother motions that could shear imprinted features from the substrate.Thus, orientation stage 250 may precisely move the template 150 about apivot point 252; thereby, eliminates shearing of desired features from asubstrate following imprint lithography.

Referring to FIG. 44, during operation of system 100, a Z-translationstage (not shown) may control the distance between template 150 and thesubstrate without providing orientation alignment. A pre-calibrationstage 260 may perform a preliminary alignment operation between template150 and the substrate surfaces to bring the relative alignment to withinthe motion range limits of orientation stage 250. In certainembodiments, pre-calibration may be required only when a new template isinstalled into the machine.

With reference to FIG. 45, therein is depicted a flexure model, denotedgenerally as 300, useful in understanding the principles of operation ofa fine decoupled orientation stage, such as orientation stage 250.Flexure model 300 may include four (4) parallel joints: joints 1, 2, 3and 4, that provide a four-bar-linkage system in its nominal and rotatedconfigurations. Line 310 may pass though joints 1 and 2. Line 312 maypass through joints 3 and 4. Angles α₁ and α₂ may be selected so thatthe compliant alignment (or orientation axis) axis lies substantially onthe template-wafer interface 254. For fine orientation changes, rigidbody 314 between Joints 2 and 3 may rotate about an axis depicted byPoint C. Rigid body 314 may be representative of rigid bodies 170 and206 of flexure members 126 and 128.

Mounting a second flexure component orthogonally onto the first one (asdepicted in FIG. 43) may provide a device with two decoupled orientationaxes that are orthogonal to each other and lie on the template-substrateinterface 254. The flexure components may be adapted to have openings toallow a curing agent (e.g., UV light) and a sensing agent (e.g., for gapsensing and/or overlay alignment sensing) to pass through the template150.

The orientation stage 250 may be capable of fine alignment and precisemotion of template 150 with respect to a substrate. Ideally, theorientation adjustment may lead to negligible lateral motion at theinterface and negligible twisting motion about the normal to theinterface surface due to selectively constrained high structuralstiffness. Another advantage of flexure members 126, 128 with flexurejoints 160, 162 may be that they may not generate particles asfrictional joints may. This may be an important factor in the success ofan imprint lithography process as particles may be particularly harmfulto such processes.

Due to the need for fine gap control, embodiments presented herein mayrequire the availability of a gap sensing method capable of measuringsmall gaps of the order of 500 nm or less between the template andsubstrate. Such a gap sensing method may require a resolution of about50 nanometers, or less. Ideally, such gap sensing may be provided inreal-time. Providing gap sensing in real-time may allow the gap sensingto be used to generate a feedback signal to actively control theactuators.

In an embodiment, a flexure member having active compliance may beprovided. For example, FIG. 46 depicts a flexure member, denotedgenerally as 400, including piezo actuators. Flexure member 400 may becombined with a second flexure member to form an active orientationstage. Flexure member 400 may generate pure tilting motions with nolateral motions at the template-substrate interface. Using such aflexure member, a single overlay alignment step may allow the imprintingof a layer on an entire semiconductor wafer. This is in contrast tooverlay alignment with coupled motions between the orientation andlateral motions. Such overlay alignment steps may lead to disturbancesin X-Y alignment, and therefore may require a complicated field-to-fieldoverlay control loop to ensure proper alignment.

In an embodiment, flexure member 250 may possess high stiffness in thedirections where side motions or rotations are undesirable and lowerstiffness in directions where necessary orientation motions aredesirable. Such an embodiment may provide a selectively compliantdevice. That is, flexure member 250 may support relatively high loadswhile achieving proper orientation kinematics between the template andthe substrate.

With imprint lithography, it may be desirable to maintain a uniform gapbetween two nearly flat surfaces (i.e., the template and the substrate).Template 150 may be made from optical flat glass to ensure that it issubstantially flat on the bottom. The template may be patterned usingelectron beam lithography. The substrate (e.g., a semiconductor wafer),however, may exhibit a “potato chip” effect resulting in micron-scalevariations on its topography. Vacuum chuck 478 (as shown in FIG. 47),may eliminate variations across a surface of the substrate that mayoccur during imprinting.

Vacuum chuck 478 may serve two primary purposes. First, vacuum chuck 478may be utilized to hold the substrate in place during imprinting and toensure that the substrate stays flat during the imprinting process.Additionally, vacuum chuck 478 may ensure that no particles are presenton the back of the substrate during processing. This may be especiallyimportant to imprint lithography, as back-side particles may createflatness problems that ruin the device and decrease production yields.FIGS. 48A and 48B illustrate variations of a vacuum chuck suitable forthese purposes according to two embodiments.

In FIG. 48A, a pin-type vacuum chuck 450 is shown as having a largenumber of pins 452. It is believed that vacuum chuck 450 may eliminate“potato chip” effects as well as other deflections on the substrateduring processing. A vacuum channel 454 may be provided as a means ofapplying vacuum to the substrate to keep it in place. The spacingbetween the pins 452 may be maintained such that the substrate will notbow substantially from the force applied through vacuum channel 454. Atthe same time, the tips of pins 452 may be small enough to reduce thechance of particles settling on top of them.

FIG. 48B depicts a groove-type vacuum chuck 460 with a plurality ofgrooves 462 across its surface. Grooves 462 may perform a similarfunction to pins 454 of the pin-type vacuum chuck 450. As shown, grooves462 may take on either a wall shape 464 or a smooth curved cross section466. The cross section of grooves 462 for groove-type vacuum chuck 462may be adjusted through an etching process. Also, the space and size ofeach groove may be as small as hundreds of microns. Vacuum flow to eachof grooves 462 may be provided through fine vacuum channels acrossmultiple grooves that run in parallel with respect to the chuck surface.The fine vacuum channels may be formed along with grooves through anetching process.

FIG. 47 illustrates the manufacturing process for both of pin-typevacuum chuck 450 and groove-type vacuum chuck 460. Using optical flat470, no additional grinding and/or polishing steps may be needed forthis process. Drilling at determined locations on the optical flat 470may produce vacuum flow holes 472. Optical flat 470 may then be maskedand patterned 474 before etching 476 to produce the desired features(e.g., pins or grooves) on the upper surface of the optical flat. Thesurface of optical flat 470 may then be treated 479 using well-knownmethods.

As discussed above, separation of template 150 from the imprinted layermay be a critical, final step in the imprint lithography process. Sincethe template 150 and substrate may be almost perfectly parallel, theassembly of the template, imprinted layer, and substrate leads to asubstantially uniform contact between near optical flats. Such a systemmay usually require a large separation force. In the case of a flexibletemplate or substrate, the separation may be merely a “peeling process.”However, a flexible template or substrate may be undesirable from thepoint of view of high-resolution overlay alignment. In case of quartztemplate and silicon substrate, the peeling process may not beimplemented easily. However, separation of the template from animprinted layer may be performed successfully by a “peel and pull”process. A first peel and pull process is illustrated in FIGS. 49A, 49B,and 49C. A second peel and pull process is illustrated in FIGS. 50A,50B, and 50C. A process to separate the template from the imprintedlayer may include a combination of the first and second peel and pullprocesses.

For clarity, reference numerals 12, 18, 20, and 40 are used in referringto the template, transfer layer, substrate, and curable substance,respectively, in accordance with FIGS. 1A and 1B. After curing of thesubstance 40, either the template 12 or substrate 20 may be tilted tointentionally induce an angle 500 between the template 12 and substrate20. Orientation stage 250 may be used for this purpose. Substrate 20 isheld in place by vacuum chuck 478. The relative lateral motion betweenthe template 12 and substrate 20 may be insignificant during the tiltingmotion if the tilting axis is located close to the template-substrateinterface. Once angle 500 between template 12 and substrate 20 is largeenough, template 12 may be separated from the substrate 20 using onlyZ-axis motion (i.e. vertical motion). This peel and pull method mayresult in desired features 44 being left intact on the transfer layer 18and substrate 20 without undesirable shearing.

A second peel and pull method is illustrated in FIGS. 50A, 50B, 50C. Inthe second peel and pull method, one or more piezo actuators 502 may beinstalled adjacent to the template. The one or more piezo actuators 502may be used to induce a relative tilt between template 12 and substrate20 (FIG. 50A). An end of piezo actuator 502 may be in contact withsubstrate 20. Thus, if actuator 502 is enlarged (FIG. 50B), template 12may be pushed away from substrate 20; thus inducing an angle betweenthem. A Z-axis motion between the template 12 and substrate 20 (FIG.50C), may then be used to separate template 12 and substrate 20. An endof actuator 502 may be surface treated similar to the treatment of thelower surface of template 12 in order to prevent the imprinted layerfrom sticking to the surface of the actuator.

In summary, embodiments presented herein disclose systems, processes andrelated devices for successful imprint lithography without requiring theuse of high temperatures or high pressures. With certain embodiments,precise control of the gap between a template and a substrate on whichdesired features from the template are to be transferred may beachieved. Moreover, separation of the template from the substrate (andthe imprinted layer) may be possible without destruction or shearing ofdesired features. Embodiments herein also disclose a way, in the form ofsuitable vacuum chucks, of holding a substrate in place during imprintlithography. Further embodiments include, a high precision X-Ytranslation stage suitable for use in an imprint lithography system.Additionally, methods of forming and treating a suitable imprintlithography template are provided.

While this invention has been described with references to variousillustrative embodiments, the description is not intended to beconstrued in a limiting sense. Various modifications and combinations ofthe illustrative embodiments as well as other embodiments of theinvention, will be apparent to persons skilled in the art upon referenceto the description. It is, therefore, intended that the appended claimsencompass any such modifications or embodiments.

1. A method of determining a spacing between a template and a substratespaced-apart from the template, defining a region therebetween having anindex of refraction associated therewith, the method comprising:impinging incident light upon the region by propagating the incidentlight along a path having a plurality of indices of refractionassociated therewith, including the index of refraction, to formmonitoring light; and determining from the monitoring light, a measureddimension of the region by ascertaining a wavenumber associated with themonitoring light that is a function of a wavelength of the monitoringlight and the index of refraction.
 2. The method of claim 1, furthercomprising determining an error signal, wherein the error signalcorresponds to a difference between a desired dimension of the regionand a measured dimension of the region.
 3. The method of claim 1,further comprising determining an error signal, wherein the error signalcorresponds to a difference between a desired dimension of the regionand a measured dimension of the region; and sending the error signal toat least one actuator, wherein the at least one actuator is configuredto adjust the spacing between the template and the substrate in responseto the difference.
 4. The method of claim 1, further comprising makingplurality of dimensional measurements of the region at differinglocations and determining whether the template and the substrate aresubstantially parallel based on the plurality of dimensionalmeasurements.
 5. The method of claim 4, further comprising determiningparallelism between the template and the substrate in response to theplurality of dimensional measurements.
 6. The method of claim 4, furthercomprising dynamically adjusting an orientation between the template andthe substrate to maintain parallelism therebetween.
 7. The method ofclaim 1, further comprising making a plurality of dimensionalmeasurements of the region at 3 or more non-colinear locations anddetermining whether the template and the substrate are substantiallyparallel based on the plurality of dimensional measurements.
 8. Themethod of claim 7, further comprising determining an error signal,wherein the error signal corresponds to a relative movement between thetemplate and the substrate required to bring the template and thesubstrate into a substantially parallel configuration.
 9. The method ofclaim 7, further comprising determining an error signal, wherein theerror signal corresponds to a relative movement between the template andthe substrate required to bring the template and the substrate into asubstantially parallel configuration; and sending the error signal to atleast one actuator, wherein the at least one actuator is configured toadjust the relative position of the template and the substrate toachieve a substantially parallel configuration.
 10. The method of claim1, wherein determining further comprises monitoring variations in anintensity of the monitored light across various wavelengths.
 11. Themethod as recited in claim 1, wherein the incident light comprises aplurality of wavelengths.
 12. The method as recited in claim 11, whereindetermining further includes obtaining data representative of anintensity of at least some of the wavelengths associated with themonitoring light.
 13. The method as recited in claim 1, wherein themonitoring light comprises reflected light.
 14. The method as recited inclaim 1, wherein the region comprises a material, with the materialhaving said index of refraction.
 15. The method as recited in claim 1,wherein the region comprises a material, with the material substantiallyfilling the region.
 16. The method as recited in claim 1, whereindetermining further includes ascertaining the dimension of the region bea function of an intensity of the monitoring light.
 17. The method asrecited in claim 1, wherein the template is a patterned template. 18.The method as recited in claim 1, wherein the template is asubstantially planar template.
 19. The method as recited in claim 1,wherein the optical characteristics include an intensity of themonitoring light.
 20. A method of determining a spacing between atemplate and a substrate, the method comprising: positioning thetemplate in a spaced relationship with respect to the substrate defininga gap therebetween, with a material being disposed in the gap and havingan index of refraction associated therewith; applying incident light tothe template and the substrate; monitoring light reaching an interfaceof the template with the material, defining monitored light; anddetermining a magnitude of the spacing between the template and thesubstrate based on the monitored light by obtaining data representativeof optical properties of the monitored light, with the magnitude being afunction of optical characteristics of the material and a wavelength ofthe monitored light.
 21. The method of claim 20, further comprisingdetermining an error signal, wherein the error signal corresponds to adifference between a desired distance between the template and thesubstrate and the spacing between the template and the substrate. 22.The method of claim 20, further comprising determining an error signal,wherein the error signal corresponds to a difference between a desireddistance between the template and the substrate and the spacing betweenthe template and the substrate; and sending the error signal to at leastone actuator, wherein the at least one actuator is configured to adjustthe spacing between the template and the substrate.
 23. The method ofclaim 20, further comprising determining the spacing between thetemplate and the substrate at a plurality of locations and determiningwhether the template and the substrate are substantially parallel basedon the plurality of spacing determinations.
 24. The method of claim 23,further comprising determining an error signal, wherein the error signalcorresponds to a relative movement between the template and thesubstrate required to bring the template and the substrate into asubstantially parallel configuration.
 25. The method of claim 23,further comprising determining an error signal, wherein the error signalcorresponds to a relative movement between the template and thesubstrate required to bring the template and the substrate into asubstantially parallel configuration; and sending the error signal to atleast one actuator, wherein the at least one actuator is configured toadjust the relative position of the template and the substrate toachieve a substantially parallel configuration.
 26. The method of claim20, further comprising determining the spacing between the template andthe substrate at 3 or more non-colinear locations and determiningwhether the template and the substrate are substantially parallel basedon the 3 or more spacing determinations.
 27. The method of claim 26,further comprising determining an error signal, wherein the error signalcorresponds to a relative movement between the template and thesubstrate required to bring the template and the substrate into asubstantially parallel configuration.
 28. The method of claim 26,further comprising determining an error signal, wherein the error signalcorresponds to a relative movement between the template and thesubstrate required to bring the template and the substrate into asubstantially parallel configuration; and sending the error signal to atleast one actuator, wherein the at least one actuator is configured toadjust the relative position of the template and the substrate toachieve a substantially parallel configuration.
 29. The method of claim20, wherein monitoring light reflected from the template and thesubstrate further comprises monitoring variations in intensity of themonitored light across various wavelengths.
 30. The method as recited inclaim 20, wherein the incident light comprises a plurality ofwavelengths.
 31. The method as recited in claim 30, wherein determiningthe magnitude further includes obtaining data representative of anintensity of at least some of the wavelengths associated with themonitored light.
 32. The method as recited in claim 20, wherein themonitored light comprises reflected light.
 33. The method as recited inclaim 20, wherein the index of refraction and the wavelength of themonitored light define a wavenumber, with the magnitude further being afunction of the optical properties of the monitored light correspondingto the wavenumber.
 34. The method as recited in claim 20, wherein theoptical characteristics of the material include the index of refraction.35. The method as recited in claim 20, wherein the materialsubstantially fills the gap.
 36. The method as recited in claim 20,wherein the template is a patterned template.
 37. The method as recitedin claim 20, wherein the template is a substantially planar template.38. The method as recited in claim 20, wherein the optical properties ofthe monitored light include an intensity of the monitored light.
 39. Amethod of determining a spacing between a template and a substrate, witha material being disposed between the template and the substrate, themethod comprising: positioning the template in a spaced relationshipwith respect to the substrate defining a gap therebetween, with saidmaterial being disposed in said gap and having an index of refractionassociated therewith; applying light to the template and the substrate,wherein the light comprises a plurality of wavelengths; monitoring lightreflected from a surface of the template and the substrate definingmonitored light; and determining a magnitude of the spacing between thetemplate and the substrate based on the monitored light by obtainingdata representative of an intensity of at least some of the wavelengthsassociated with the monitored light arid determining a wavenumberassociated therewith, wherein the wavenumber is a function of the indexof refraction and the wavelength of the monitored light, with saidmagnitude being a function of the wavenumber.
 40. The method of claim39, further comprising determining an error signal, wherein the errorsignal corresponds to the difference between a desired distance betweenthe template and the substrate and the magnitude.
 41. The method ofclaim 39, further comprising determining an error signal, wherein theerror signal corresponds to the difference between a desired distancebetween the template and the substrate and the magnitude; and sendingthe error signal to at least one actuator, wherein the at least oneactuator is configured to adjust the spacing between the surface of thetemplate and the substrate.
 42. The method of claim 39, wherein thetemplate comprises a plurality of recesses defined on a surface thereof.43. The method of claim 39, wherein the template comprises a pluralityof recesses defined on a surface thereof, wherein the recesses are of aknown depth.
 44. The method of claim 39, wherein the template comprisesa plurality of recesses defined on a surface thereof and whereinapplying light to the template and the substrate comprises passing thelight through one or more of the recesses.
 45. The method of claim 39,wherein the template comprises a plurality of recesses defined on asurface thereof and wherein a depth of each recess is at least ¼ of amean wavelength of the light applied to the template and the substrate.46. The method of claim 39, further comprising determining the distancebetween the template and the substrate at a plurality of locations anddetermining whether the template and the substrate are substantiallyparallel based on the plurality of distance determinations.
 47. Themethod of claim 46, further comprising determining an error signal,wherein the error signal corresponds to a relative movement between thetemplate and the substrate required to bring the template and thesubstrate in to a substantially parallel configuration.
 48. The methodof claim 46, further comprising determining an error signal, wherein theerror signal corresponds to a relative movement between the template andthe substrate required to bring the template and the substrate in to asubstantially parallel configuration; and sending the error signal to atleast one actuator, wherein the at least one actuator is configured toadjust the relative position between the template and the substrate toachieve a substantially parallel configuration.
 49. The method of claim39, wherein the template is a patterned template.